Laser-assisted evaporation has been used previously to deposit thin films of superconducting materials such as YBa.sub.2 Cu.sub.3 O.sub.7. The deposition process utilizes a high power, pulsed excimer laser to ablate superconducting material from the face of a superconducting pellet and to deposit the same onto a nearby substrate.
As shown in FIG. 1, a vacuum chamber 1 is coupled to a pump 2. A laser beam 3 enters the chamber 1, after passing through a focusing lens, through a quartz window 5 and strikes a pellet 6 of superconductor material. The pellet 6 is mounted about 1-5 cm from a substrate 8, which is heated by heater 9, while a vacuum of about 1.times.10.sup.-6 torr is maintained. The beam 3 of pulsed 248 nm light is generated by a KrF laser source. A white plasma is produced at the surface of the pellet 6 and a visible plume 7 of excited ejected particles extends toward substrate 8. Typical resulting film thicknesses range from 0.1 to 3 .mu.m.
By ablating a high transition temperature superconducting composition, a superconducting thin film may be obtained on a suitable substrate as described above. However, the ability to vary the film composition in a controlled manner has been identified as a problem, particularly for research and development purposes.
In the past, control of the final film composition was accomplished by changing the mix of a single target. This approach has involved preparation of many pellets of varying composition requiring days or weeks before a determination could be made regarding the composition of the deposited film. Variability had to be traced back through target preparation, film deposition conditions and film analysis.